The present invention relates to range finding equipment for use in apparatus such as still cameras or motion picture and television cameras and more particularly to an improvement to the type of range determination apparatus which utilizes two optical paths for forming two images on a pair of detectors with the relative spacing of the images on the detectors being indicative of the range to a remote object and in which a moving grating or grid structure is employed to periodically interrupt the images received by the detectors so that their outputs are variable electrical signals whose phase relationship becomes indicative of the range to the remote object.
In the art of automatic range finding equipment, a number of systems have been proposed for automatically determining the distance from an optical system to a remote object. One such system employs apparatus for the automatic parallax determination in connection with a stereoscopic optical system in which images of the object are focused upon two detectors from two separate optical transmission means that are spaced apart a distance forming the baseline of a triangulation scheme. If, for example, the object were at infinity, the images on the two detectors would be the same and the outputs of the detectors would be equal. If the object were to move closer to the system, then the image on at least one of the detectors would move with respect to the image on the other so that the output of the detectors would change indicating an "out-of-focus" condition. In order to detect the change of position of the image on one detector with respect to the other, it has also been proposed that a moveable grating, chopper, grid or prism be interposed in the light path to each detector so that the output of the detectors becomes a varying signal, for example, sinusoidal. At infinity, the phase of the two sinusoidal signals from the detectors would be coincident, but as the object moved closer to the optical system and one image moved with respect to the other, the phase of the signals from the detectors would change. It has further been proposed that phase detecting apparatus, connected to receive the outputs of the detectors, may be employed to produce a signal indicative of the difference in the images of the two detectors and thus of the range to the object. This signal may be used to adjust one of the optical systems to bring the images back into coincidence and the phase of the output signals from the detectors back into equality or the signal may be used to position an indicator or other device so as to provide an indication of the range to the object.
A difficulty has been encountered in the prior art systems due to what is known as "edge effects". A major cause of this is the artificial reduction in light from the subject being detected due to the limit or edge of the sensing or light measuring system. The scanning system will see or detect this limit or edge and produce a resulting "edge signal". The output signal will be a combination of the desired information signal and the edge signal. The combination signal can be significantly in error due to the combined edge component. The elimination of the edge signal improves the system performance and accuracy. Another edge effect problem occurs when one detector sees a slightly different scene area than the other one due, for example, to slight system misalignment or subject distance. If a bright object were just on the edge of the image on one detector but not on the edge of the other due, then the output of the one detector would be different than the output of the other even though the objects might be in a proper focus position.